1. Field of the Invention
The invention relates to a process for the preparation of 1,3-diacyl-4-imidazolin-2-ones and to their use for cycloadditions.
2. Discussion of the Prior Art
The preparation of 1,3-diacetyl-4-imidazolin-2-one is known from J.Chem.Soc. 95, 1329 (1909). Thus, the reaction of 4-imidazolin-2-one with acetic anhydride, on heating, gives 1,3-diacetyl-4-imidazolin-2-one. However, 4-imidazolin-2-one required as the starting compound for this reaction is difficult to obtain and in larger amounts, in particular, is hardly accessible. Thus, for example, the reaction of .alpha.-aminoacetaldehyde diethylacetal with cyanic acid, followed by cyclisation, gives 4-imidazolin-2-one, but this reaction sequence is greatly dependent on the reaction parameters (concentration, temperature and the like) (J.Amer.Chem.Soc. 68, 2351 (1946)) and can only be carried out on a sizeable scale with substantial losses in yield.
The reaction of tartaric acid or dihyroxymaleic acid with urea in concentrated sulphuric acid or oleum to give 4-imidazolin-2-one-4-carboxylic acid, followed by decarboxylation (J.Amer.Chem. Soc. 54, 3413 (1932), C. A. 78, 58. 318 m (1973)) is also technically rather unsuitable for the preparation of sizeable amounts of 4-imidazolin-2-one (large volumes of reaction solution, and elimination of CO.sub.2). Since furthermore, during the subsequent esterification, unconverted 4-imidazolin-2-one or only partially esterified 4-imidazolin-2-one, such as, for example, 1-acetyl-4-imidazolin-2-one, specifically greatly retards or even inhibits photochemical cycloadditions with the 1,3-diacyl-4-imidazolin-2-ones (Chem.Ber. 100, 3961 (1967); 101, 3688 (1968)) it was desirable to provide a process for the synthesis of 1,3-diacyl-4-imidazolin-2-ones, especially of 1,3-diacetyl-4-imidazolin-2-one, in which the two acyl radicals are already present in the starting compound and do not undergo any change during the reaction to give the 1,3-diacyl-4-imidazolin-2-one.